1. Field of the Invention
The invention concerns an installation device for a gradient coil module in a magnetic resonance tomography apparatus.
2. Description of the Prior Art
A magnetic resonance tomography apparatus is an imaging medical diagnostic modality. A magnetic resonance tomography apparatus has a basic field magnet to provide a basic magnetic field. This basic field is overlaid with at least one magnetic field gradient. This occurs by means of a gradient coil module that is arranged in the basic field. For example, the design of such a gradient coil module is described in DE 197 21 985 A1, DE 197 22 211 A1 and DE 100 32 836 C1. Such a high-current module has multiple layers of gradient coils in order to generate three magnetic field gradients situated perpendicularly to one another. Furthermore, at least one cooling layer is provided to transport away the heat produced by the gradient coils. This cooling layer is arranged between two layers of gradient coils. The layers of gradient coils and the at least one cooling layer are cast with one another in a casting compound made of plastic and together form the gradient coil module.
The gradient coil module is installed in a channel-like gradient coil receptacle of the magnetic resonance tomography apparatus. An exchange or a disassembly and reassembly off the gradient coil module is necessary at specific time intervals for maintenance purposes.
In a conventional magnetic resonance tomography apparatus with a magnetic field strength of up to 3 Tesla, the basic field magnet is deactivated for the disassembly. The deactivation and reactivation of the basic magnetic field takes approximately four hours. In a magnetic resonance tomography apparatus based on the ultra-high frequency technique (UHF) with a magnetic field strength of the basic field magnet of up to over 7 Tesla, such deactivation and reactivation are associated with a high cost and time expenditure, since multiple days must be planned for the deactivation and reactivation of the basic field magnet. The magnetic resonance tomography apparatus is not available for measurements in this time period, but consumes a large amount of electrical energy. Therefore, in particular for a magnetic resonance tomography apparatus based on the UHF technique, it is typical to uninstall and reinstall the gradient coil module with the basic field magnet activated in order to keep the downtime of the magnetic resonance tomography apparatus as small as possible.
The installation and uninstallation typically occur with the use of a number of height-adjustable supports (stands) by means of which an installation girder is introduced into the gradient coil receptacle. A travel sled is borne on the installation girder such that it can be longitudinally displaced. After releasing the mountings by means of which the gradient coil module is fastened in the gradient coil receptacle, the inner wall of the gradient coil module is braced on the travel sled so that the gradient coil module can be pulled out from the gradient coil receptacle with the travel sled. The positioning of the installation girder and the extraction of the gradient coil module by means of the travel sled are associated with a high personnel cost, since the individual supports and the installation girder are not permanently connected with one another, and must be assembled. For a magnetic resonance tomography apparatus with large dimensions and a deep gradient coil receptacle, moreover, the insertion of a long installation girder is additionally necessary in order to reach to the installation location of the gradient coil module. The alignment of a long installation girder is complicated.
An installation girder produced from one beam always has a residual magnetism. Therefore, with an activated basic magnetic field, the installation girder is pulled from this field such that the disassembly and reassembly of the gradient coil module is made more difficult. This difficulty in particular occurs in UHF systems. Even a fixing of the installation girder to the supports by means of screw clamps or the like only slightly improves the mechanical stability of the installation device. Furthermore, the installation girder bends under the weight of the gradient coil module, such that the sliding of the gradient coil module into the gradient coil receptacle by means of the travel sled is hindered. Bracing of the installation girder inside the gradient coil receptacle is not possible.